Electrically conductive polymer gel itself may be used as an electrolytic capacitor and a solid electrolyte solution for an electric capacitor, battery, etc., or it may be used by formulating it to adhere to an electrode element of a humidity sensor, a pressure sensor, etc., and as an organism-use electrode.
In the medical field, in order to conduct an appropriate treatment, the potential of an organism is often measured by an electrocardiogram, electromyogram, brain waves, etc. Electrical treatment by transmitting an electric signal into the organism also increases. In the above measurement or treatment, the organism-use electrode which serves as a medium between the organism and an external equipment plays an important role.
For example, when measuring the potential of an organism, the organism-use electrode must be brought in direct contact with a part of the organism in order to derive an effective use of a weak electric signal to be transmitted to the electrocardiogram, etc. However, direct contact between the electrode and the skin of the organism does not permit a desirable electric junction. An unstable junction between the organism-use electrode and the skin of the organism causes complications with respect to potential and impedance. Thus, an electric signal cannot be detected accurately.
In order to counteract the above problem, the following method has been proposed: the organism-use electrode is connected to a part of the skin of the organism through an electrically conductive polymer gel which permits an electric signal to be sent from the organism to the external equipment by making the organism-use electrode in stable contact with the skin of the organism without stimulating it.
In the above method, for example, electrically conductive polymer gel from the acrylic acid sodium series with a property of shape retention may be used. This electrically conductive polymer gel can be formed beforehand into predetermined thickness and shape, and it is used by forming it to adhere to an electrode element to be one integral part. The above organism-use electrode is convenient since it is disposable and it eliminates the application process.
However, the above electrically conductive polymer gel from the acrylic acid sodium series presents the following problems:
For example, when measuring an electrocardiogram, the current flow of an electrocardiogram signal is electromotive in heart.fwdarw.tissue.fwdarw.skin.fwdarw.electrically conductive polymer gel.fwdarw.electrode element.fwdarw.lead wire.fwdarw.amplifier in the electrocardiogram.fwdarw.lead wire.fwdarw.electrode element.fwdarw.electrically conductive polymer gel.fwdarw.skin.fwdarw.tissue.fwdarw.electromotive in the heart. In this case, current flows from the organism to the electrically conductive polymer gel as ions move. On the other hand, current flows from the electrode element to the amplifier by free electrons. Additionally, ions and free electrons can be freely exchanged between the surface of the electrode element and the electrically conductive polymer gel.
The electrically conductive polymer gel from the acrylic acid sodium series has the property of being hydrophilic in nature, and the polymer thereof is electrolytic and electrically conductive. Thus, the complete conjunction between the electrically conductive polymer gel and metal series in general cannot be achieved due to an electric repulsion between the electrode element of metal series in general. Moreover, an exchange between ions and free electrons cannot be fully carried out. As a result, the impedance at the interface increases, and precise measurement of the electrical phenomenon of the organism cannot be ensured.
The Japanese Laid-Open Patent Publication 15728/1981 (Tokukaisho 56-15728) discloses an electrically conductive material which includes 70% by weight glyceline and thorium chloride in nonelectrolyte polyacrylamide. However, this electrically conductive material is hard and shows large impedance since it does not include liquid of low viscosity such as water.
In order to counteract the above problem, the Japanese Examined Laid-Open Patent Publication 22839/1986 (Tokukaisho 61-22839) discloses an electrically conductive polymer gel which includes sucrose and a large quantity of water in the polyacrylamide. Having nonelectrolyte, shape retentive and flexible nature, the junction between the electrode element and the skin of the organism can be improved, thereby reducing the impedance.
However, this electrically conductive polymer gel presents another problem: sucrose cannot suppress the evaporation of water, resulting in an increase in the impedance as it dries out in relatively short periods of time. Thus, the electrical phenomenon in the organism cannot be measured accurately over longer periods of time.
Moreover, since the tackiness of the electrically conductive polymer gel is low, a desirable adhesive property to the electrode element cannot be ensured and a part of gel may separate from skin or from the electrode element while being used. Moreover, a hot spot is likely to appear between the gel and the skin. In order to prevent the separation of the gel and the appearance of the hot spot, it is required to restrict the degree of freedom of the target organism.
For the electrode element, carbon, Ag/AgCl, german silver (alloy consisting of Cu, Ni or Zn) may be used according to the use for which it is intended. However, the component Cu of german silver is corroded by water, electrolyte, etc., and the corrosion of Cu is expedited by the acrylamide of the electrically conductive polymer gel, resulting in an increase of the impedance. For this reason, the electrode cannot be used many times. Moreover, it is not possible to form beforehand the electrode element and german silver as one integral part.